PCB Etching Process — Step by Step
A complete printed circuit board is the output of 14 sequential process steps — from raw copper-clad laminate to a tested, finished board ready for component assembly. This guide walks through each step with the chemistry, machine, and tolerance data you need to spec the right line for your PCB production.
The PCB etching process is one step in a 14-step production line, but it's the one that defines the circuit pattern. Etching is the chemical dissolution of bare copper — leaving only the copper that the photoresist protected. The other 13 steps exist to prepare the panel for etching, then to finish and test the board after etching. This guide walks the full sequence so you understand which steps are critical, which are forgiving, and where the GE-series equipment fits.
From raw laminate to tested PCB
1. Board cutting
The raw copper-clad laminate (FR-4, CEM-1, or high-frequency substrate) is cut to a workable panel size — typically 460 × 610 mm or 510 × 610 mm for a standard PCB line. The cut is by laser (GE-LCB6080, 0.05-0.15 mm kerf) or by high-speed saw. No chemistry involved.
2. CNC drilling & routing
Through-holes, vias, and tooling holes are drilled with a multi-spindle CNC. The drill hits a registration target on the panel so that the through-holes line up with inner-layer pads. Typical spindle count: 2-6, drill diameter 0.15-6.5 mm. Tolerance on hole position: ±0.025 mm. After drilling, holes are deburred with the GE-B650 brushing grinding machine (for prototype) or the GE-MB650 / GE-GBD650 (for production).
3. PTH & copper plating
The drilled holes are chemically metallised with electroless copper, then copper is electroplated onto the holes and any inner-layer exposed copper. The PTH bath is held at 25-30 °C with strict chemistry control (NaOH, formaldehyde, copper sulphate, EDTA). Plating thickness: 20-30 µm in the hole barrel.
4. Photoresist coating
The panel is laminated with dry-film photoresist (typically 25-50 µm thick) or coated with liquid photoresist. Lamination temperature: 105-115 °C, lamination pressure: 3-5 bar. The resist protects the copper pattern that will remain after etching.
5. Exposure
The artwork (1:1 photo-tool or direct LDI) is exposed onto the resist with UV light. The exposed resist hardens (negative resist) or softens (positive resist) in the pattern. Exposure dose: 80-120 mJ/cm² for standard dry-film. Modern lines use 4-CCD or 8-CCD camera alignment for ±0.005 mm layer-to-layer registration.
6. Developing
The unexposed resist is washed off in 1% Na₂CO₃ solution at 30-32 °C, revealing the bare copper that will be etched. Developing is a spray process — the developer is sprayed onto the panel, the unexposed resist dissolves, and the panel is rinsed. Developing time: 60-90 seconds.
7. Etching
The bare copper is dissolved by ferric chloride (FeCl₃) or cupric chloride (CuCl₂) chemistry sprayed onto both sides of the panel. Etch rate: 40-60 µm/min for FeCl₃ at 50 °C, 50-70 µm/min for CuCl₂. Spray pressure: 1.5-2.5 bar at the manifold. Etch uniformity: ±0.02 mm across a 650 × 800 mm panel on a GE-JM spray etching line. After etching, the panel exits the chamber with the circuit pattern in copper, ready for resist stripping.
8. Resist stripping
The protective photoresist is stripped off in 3-5% NaOH solution at 50-60 °C, exposing the bare copper pattern. The stripped resist is rinsed away and the panel moves to solder mask coating. Stripping is a spray process similar to developing but with stronger chemistry.
9. Solder mask coating
Photo-imageable solder mask ink is coated onto both sides of the panel (single or double-side coater). The mask is then exposed and developed, leaving the mask only on areas where copper should be protected (everywhere except pads, vias, and the board edge). The mask is then baked at 150 °C for 60 minutes to fully cure. Common colours: green, blue, black, red.
10. Legend (silk screen)
White or yellow epoxy ink is screen-printed onto the cured solder mask to print the component reference designators (R1, C2, U3), the board outline, and any logos. The legend is then baked at 150 °C for 30 minutes.
11. Surface finish
Exposed copper pads are finished to keep them solderable. Three common finishes:
- HASL (Hot Air Solder Leveling) — dip the panel in molten solder (or lead-free SAC305), then level with hot-air knives. Cheapest, but uneven surface.
- OSP (Organic Solderability Preservative) — apply a thin organic coating that protects copper until soldering. Flat surface, fine-pitch compatible, but limited shelf life.
- ENIG (Electroless Nickel Immersion Gold) — plate 3-5 µm nickel then 0.05-0.1 µm gold. Best for fine-pitch, BGA, and wire bonding. Most expensive.
12. V-groove scoring
For boards that will be panelised and depanelised after assembly, V-shaped grooves are scored on both top and bottom surfaces along the depanelisation line. The V-groove depth is 30% of board thickness on each side, leaving 40% in the middle to be snapped after assembly.
13. Final cleaning
The finished board is washed and dried to remove flux residue, dust, and contamination from the previous steps. DI water rinse, hot-air dry. The output is a clean, finished PCB ready for electrical test.
14. Electrical test
Every net on the PCB is tested for continuity (no opens) and isolation (no shorts). For prototype and small batch, a high-speed flying-probe tester is used. For volume production, a bed-of-nails fixture tester is faster. Failed boards are marked and reworked or scrapped.
Process parameters that make or break PCB etching
Of the 14 steps, the etching step is the most sensitive to chemistry and process control. Three parameters make or break the result:
- Etchant specific gravity. FeCl₃ should be held at 38-42° Baumé. Below 35°, the etch rate drops and undercut increases. Above 45°, the etchant becomes viscous and the spray pattern degrades.
- Spray pressure. 1.5-2.5 bar at the manifold. Below 1.2 bar, the boundary layer on the copper surface becomes unstable and etch uniformity suffers. Above 3.0 bar, the spray etches the resist sidewall and undercut increases.
- Temperature. 45-55 °C. Below 40°, the etch rate is too slow. Above 60°, the FeCl₃ starts to attack the resist and the etch becomes uncontrollable.
A modern PCB etching line holds these three parameters in closed-loop control with continuous ORP and density monitoring. The GE-JM spray etching line ships with all three loops integrated.
PCB Etching Process FAQ
The PCB etching process is the chemical dissolution of bare copper from a copper-clad laminate to leave a circuit pattern defined by photoresist. A typical PCB production line has 14 steps: board cutting, CNC drilling, deburring, PTH & copper plating, photoresist coating, exposure, developing, etching, resist stripping, solder mask coating, legend printing, baking, surface finish (HASL / OSP / ENIG), V-groove scoring, and electrical test.
The two workhorse etchants are ferric chloride (FeCl₃) and cupric chloride (CuCl₂). Ferric chloride is the all-rounder — etches copper quickly with a brown-red solution. Cupric chloride is preferred for high-volume PCB production because it can be regenerated continuously with chlorine gas or air, holding specific gravity and etch rate constant over an 8-hour shift. Ammonium persulfate is used for thin copper and fine-line PCB where a slow, controlled etch is required.
On a standard PCB etching line at 50 °C with spray agitation, FeCl₃ etches copper at 40-60 µm/min. A typical 35 µm (1 oz) copper layer clears in under a minute; a 70 µm (2 oz) layer takes 2 minutes. Cupric chloride is slightly faster, around 50-70 µm/min at 50 °C.
For standard PCB etching, the minimum line width and spacing are typically 0.075-0.1 mm (3-4 mil). For fine-line PCB, advanced etching lines hold 0.05 mm (2 mil). For HDI and any-layer PCB, the precision vertical etching line holds 0.04 mm (1.5 mil). The limitation is the photoresist resolution and the etchant's lateral attack (undercut), not the chemistry itself.
Inner layer etching is done before lamination — copper is etched on a single side of a thin copper-clad laminate, then the layers are stacked, laminated, and drilled. Outer layer etching is done after lamination and PTH — both sides of the panel are etched simultaneously, leaving the through-hole plating intact. The equipment is similar but inner layer etching has tighter tolerance (typically ±10% of trace width) while outer layer etching tolerates more variation because the holes carry the inter-layer connection.
A typical PCB etching cycle (drilling through final test) takes 90-180 minutes depending on layer count and complexity. The etching step itself is just 6-12 minutes per panel. Most of the cycle time is upstream and downstream — drilling 3-5 minutes, PTH plating 30-45 minutes, exposure + developing 5-10 minutes, solder mask 10-15 minutes, surface finish 5-15 minutes, V-groove 2-3 minutes, electrical test 3-5 minutes.
PCB etching uses FeCl₃ or CuCl₂ to remove copper from a copper-clad laminate, leaving the dielectric (FR-4) as the base. Chemical milling uses the same chemistries (or alkaline etchants) to remove metal from a solid metal sheet — typically stainless steel, copper or aluminium. The equipment is similar; the difference is the starting material and the photoresist process. See our chemical milling equipment range for details.
Use ferric chloride (FeCl₃) for low to medium volume PCB production, prototype work, and lines where the etchant is dumped and replaced periodically. Use cupric chloride (CuCl₂) for high-volume PCB production where you want continuous regeneration — chlorine gas is metered into the regeneration cell to convert Cu⁺ back to Cu²⁺, holding etch rate constant. Most modern PCB lines run cupric chloride because regeneration saves chemistry cost and steadies the process.